An automatic coffee machine is understood to be a machine in which the processes of grinding the coffee powder, feeding the coffee powder into the percolating chamber, the percolating process itself and the discharge of the used coffee powder as well as the discharge of the used and compressed coffee block of coffee powder is all performed automatically without needing any one of these or any other procedures to be triggered or supported by manual instruction. However, it is understood that for carrying out a cycle, the automatic coffee machine needs to be activated by pressing a button or similar means. The invention may also be used for percolator a large quantity of fresh coffee automatically.
An automatic coffee machine of the above described type is known from U.S. Pat. No. 5,007,333. The upper stopper in the percolator is in this case supported on a slide which in turn can be moved horizontally on a cover section of the flow heater, constructed as a slideway. A linear drive for moving the upper stopper backwards and forwards into the parked and stand-by positions along the axis of the tube section is provided for this. An axial drive for moving the upper stopper in the direction of the axis of the tube section is mounted on the slide and travels with it, whereby these two drives are actuated one after the other. The upper stopper is constructed in two pieces and consists of a carrier part and a partially wedge-shaped centering part which supports a single seal, on the one hand, for closing the percolating chamber, as well as for sealing the inlet of the hot water on the other. The centering part is mounted on the carrier part so that it has limited movement both axially and radially in order to enable self-centering on the upper edge of the tube section, upon which the seal is seated after centering by means of the centering part as a stop and valve seat. At the same time as doing this, the percolating chamber on the one hand, and the hot water inlet on the other, are sealed. The lower stopper, built like a piston and guided within the tube section, also has a vertical drive with a double-action, hydraulically actuated piston. With this known automatic coffee machine the exact positioning of the upper stopper on the axis of the tube section of the percolator is only possible through the two-piece construction of the upper stopper. The linear drive, moving exactly radially with respect to the axis of the tube section, must be built relatively large because the drive elements which engage with the upper stopper, as well as the associated motor, must be mounted on the side of the upper stopper facing away from the tube section in order that, for example, in the parked position, the upper opening of the tube section is not wrongly adjusted so that, for example, the coffee powder may be introduced unhindered into the internal chamber of the tube section. Owing to the large size of the design for the drive and a necessary support it is difficult to transfer the upper stopper into the stand-by position with sufficient accuracy. In addition, differing temperatures, i.e. hot or cold condition, have an expansion/contraction effect on the linear drive. The large amount of space required for this linear drive is a nuisance in many cases, especially in the case of preparing narrow subassemblies for combined machines. The slide also increases the mass to be moved. It must be driven laterally, i.e. outside its center of gravity, meaning a disadvantage, and this troublesome form of construction presupposes that the cover section of the flow heater is designed as a slideway. Further, the hydraulic vertical drive for the lower stopper requires a multiplicity of seals and solenoid valves which can lead to faults. Achieving accurate, reproducible positions for the lower stopper relative to the axis of the percolator and the controllability of these positions is also only possible to a limited degree.
Another automatic coffee machine is known from U.S. Pat. No. 2,827,845. Here too, the percolator has a tube section which is arranged with a vertical axis and partly located already in the flow heater housing so that an essentially constant discharge temperature for the coffee beverage is achieved independently from the chronological sequence of individual percolating cycles. A one-piece upper stopper is used in conjunction with this tube section, whereby said stopper is arranged so that it can move, by means of a single drive, not only radially to the axis of the tube section of the percolating chamber, but also in the direction of the axis of the tube section. The stopper itself is constructed wedge-shaped and provided with a seal which merely fulfils the function of sealing the percolating chamber at the top because the hot water inlet is provided in the area of the lower stopper. The lower stopper is also constructed wedge-shaped and provided with a seal. However, such a percolating chamber with wedge-shaped stoppers has the disadvantage that it is not possible to move these stoppers like a piston within the tube section and, for example, to pre-compress the coffee introduced in loose (powder) form into a block. Compression of the coffee until it is dry and discharge in the dry state are also not possible. By virtue of the wedge-shaped design of the two stoppers, accurate positioning relative to the axis of the tube section is only required to a limited degree.
Another automatic coffee machine is known from WO 82 01 120. The percolating chamber, comprising a stationary tube section with vertical axis, is provided there within a support plate which is connected via a construction comprising guide rods to a second support plate. Hydraulically actuated piston/cylinder units are provided in the second support plate and said units assist in moving into the tube section two piston-type stoppers at each end of the tube section or in moving said stoppers inside said tube section. Consequently, the problem of the accurate axial positioning of the stoppers does not occur here because both stoppers can only be moved axially. In addition, a pivoting funnel piece is provided which serves for introducing the ground coffee powder from the side into the percolating chamber and for discharging the block of used coffee from the percolating chamber.